This invention relates to a recording medium, more particularly to a laminated structure of a protective film, lubricative layer, etc. which are applied on the surface of the recording media of the type which contacts the magnetic head temporarily or constantly, such as magnetic recording disk or tape.
For instance, in the magnetic recording disks (hereinafter referred to as magnetic disks) used as mass storage for electronic computers, a ferromagnetic thin film with high recording density is formed on the surface of a non-magnetic substrate by sputtering or other means. Generally, a protective film made of amorphous carbon is formed on said ferromagnetic film, and a perfluoropolyether type liquid lubricant is further applied on said protective film for enhancing sliding durability and corrosion resistance by dipping into lubricant solution.
Adhesiveness of the liquid lubricant to the protective film surface exerts a great influence on sliding durability and corrosion resistance of the magnetic disk. According to the conventional dipping techniques, the liquid lubricant could be scattered by the sliding motion of the head on the magnetic disk, and also the lubricating performance could be varied greatly under a high-temperature or low-temperature condition. This is atributable to the fact that the lubricant molecules are adsorbed physically on the protective film surface and no chemical bond exists at the interface between the lubricant molecules and the protective film.
Also, the lubricant concentration or the state of protective film surface would exert a delicate influence on the lubricant build-up in the step of coating of the lubricant, making it difficult to control the thickness of the lubricant film. There also was a possibility that the liquid lubricant or the solvent be contaminated with impurities in the coating step.
Further, because of being liquid, the lubricant could gather around the head while it stayed stationary, letting the head and the magnetic-disk stick to each other to cause improper operation.
Various attempts have been made for overcoming these problems of lubricant. For instance, in Japanese Patent Application Kokai (Laid-Open) No. 61-155345, it has been proposed to apply, on the protective film, a lubricant, such as perfluoropolyether, which contains a terminal group having an anchoring function.
Said lubricant of the prior art (proposed in JPN Pat. Appln. Kokai No. 61-155345) exhibits an excellent adhesive performance when applied directly on a metal surface. However, when applied on a protective film made of amorphous carbon or a non-metallic compound such as silicon oxide, said lubricant can not bring its anchoring function into full play, resulting in a reduced adhesive performance. This can be accounted for by the fact that because of low reactivity between the terminal group of said lubricant and a non-metallic compound, there is hardly produced a solid chemical bond.
Further, it was difficult to work the lubricant molecular layer into a uniform thin film because of weak adhesive force of said molecular layer, so that said lubricant could not be applied to a magnetic disk with high recording density which disk is turned with its surface kept in contact with the head.